Injection stretch blow molding (ISBM) is a process widely used for the production of containers, such as bottles, using thermoplastic polymers. The process includes the steps of preparing a preform by injection molding and then expanding the preform to the desired final shape. In general, one distinguishes one-stage processes and two stage-processes. In the one-stage process, the steps of producing preform and expanding the preform to the desired final shape are performed in the same machine. In the two-stage process these two steps are performed in different machines, in some cases even in different geographical locations—the preform is allowed to cool to ambient temperature and is then transported to a second machine, where it is reheated and expanded to the desired final shape. Due to reasons of production speed and flexibility the two-stage process is preferred for larger production volumes.
Recent progress in development has made polypropylene a viable alternative to polyethylene terephthalate (PET) for injection stretch blow molding (ISBM). Due to their good optical properties propylene-ethylene random co-polymers are the preferred polypropylene grades.
For the injection molding of polypropylene it is well known to improve the impact performance, while also having good optical properties by the addition of a polyethylene, which has been produced using metallocene catalyst.
The polypropylenes presently used in the injection stretch blow molding applications allow the production of containers with good optical properties at industrially viable production rates. However, as compared to the other polymers used in the injection stretch blow molding polypropylene suffers from a lack of the combination of high rigidity and high ESCR, as well as high impact strength, particularly at lower temperatures. There is a need for new polyolefins having improved injection properties and blow molding properties.